Electrophysiological and optical recording techniques are used primarily to elucidate the development, differentiation and cellular distribution of physiologically important properties expressed in vitro by vertebrate CNS neurons or by fibroblasts transfected with transmitter receptor genes. Electrical studies involve direct, high-fidelity amplification of ion fluxes generated in single cells or in synaptically coupled pairs of cells maintained in monolayer culture. Optical recordings include simultaneous indirect measurements of membrane potential or of intracellular ion concentration in 5-50 cells in culture. Principal findings this year include: 1) depolarizing GABAA receptors are co-expressed with functional voltage-dependent Na+ channels and depolarizing kainic acid receptors in the earliest period of postmitotic differentiation of the rat spinal cord; 2) GABAA receptors couple to Cl-ion selective conductances in hippocampal neurons during the embryonic period; 3) GABAA receptors activated on physiologically intact early postnatal septal neurons are functionally excitatory, triggering action potentials,; 4) dose-response curves indicate that submicromolar agonist concentrations are effective and that a Hill coefficient close to 1 describes the dose-response; 5) pharmacological effects of anesthetic and naturally occurring steroids at GABAA receptors can be detected before birth on embryonic hippocampal neurons; 6) fluctuation analysis of GABAA receptor-coupled Cl-conductances shows complex, two-component kinetics of ion channel behavior both in embryonic hippocampal neurons and in fibroblasts expressing specific GABAA receptor subunit combinations; 7) septal neurons express a full complement of electrical and chemical excitability during the first week postnatal; 8) TRH activates K+-ion selective conductances in tumoral pituitary cells via 1,4,5-inositol trisphosphate- and diacylglycerol-induced mobilization of Ca2+ from intracellular stores; 9) fluctuation analyses of endogenous voltage trajectories in cultured embryonic chick spinal cord cells at the resting membrane potential reveals complex behavior suggestive of a deterministic system.